In general, in radio communication of a multipath environment, the same signal is transmitted on a plurality of paths of different routes, and thereby, on the receiving side, a mixture of direct waves and delay waves is received. As a result, intersymbol interference which becomes an obstacle to development of high speed and wideband radio communication, occurs.
For suppressing intersymbol interference, the OFDM (Orthogonal Frequency Division Multiplexing) scheme and SC (Single Carrier) scheme, which are referred to as block transmission schemes, have attracted attention in recent years. In these schemes, as shown in FIG. 1, for example, guard intervals GI1, to GI4 are inserted between symbols S1 to S4 of the signal. Guard intervals GI1 to GI4 are replications of the end portions of symbols S1 to S4 that respectively follow, and therefore the end of each guard interval and head of each symbol become a consecutive waveform and have cyclicity.
In this way, by inserting guard intervals between all symbols, the receiving side can extract a symbol portion which is not influenced by intersymbol interference, and remove the influence of a multipath environment only through linear operation. At this time, the influence of longer delay waves can be ignored by making the guard interval long, and the effect of removing the influence of multipath environment increases.
On the other hand, the guard interval is a redundant component which does not include information to be transmitted, and therefore, from the viewpoint of transmission efficiency, it is preferable to make the guard interval as short as possible. Here, Patent Document 1, for example, discloses a technique of adjusting a guard interval length in an OFDM scheme to eliminate waste.    Patent Document 1: Japanese Patent Application Laid-open No. 2004-282182